A gem, which dates originally to Duke of Nantes in 1530s, was one of several items stolen from the Napoleon collection, and later recut and created for Louis XV on his investiture into the Order of the Golden Fleece. This knightly order is one of the oldest orders in existence.
According to media story cover this order from the napoleon.org website the Order of the Golden Fleece dates from 1430. So I’m guessing there will be claims for more senior orders being in existence, but then this website blurb is for public consumption and marketing I would presume.
The 'Order of the Golden Fleece' medal awarded to the Prince Imperial - napoleon.org




